The invention relates to a semiconductor structure with active zones, and to a method for manufacturing such a semiconductor. The invention further relates to a blended-color sensor, and to a colored display that contains the semiconductor structure with the active zones.
A semiconductor structure with active zones of the type mentioned above is described in an article by I. Ozden, et al.: “A dual-wavelength indium gallium nitride quantum well light emitting diode” in Applied Physics Letters, Vol. 79, No. 16, 2001, pp 2532-2534. This article deals with a monolithic, dual wavelength (blue/green) light-emitting diode (LED) with two active indium-gallium-nitride/gallium nitride (InGaN/GaN) multiple quantum well segments. The segments are part of a single vertical epitaxial structure, in which a p++/n++/InGaN/GaN tunnel junction is inserted between the LED's. The segments emit at 470 nm and 535 nm, respectively.
EP-A-1 403 935 describes a light-emitting diode with a first active zone, a second active zone and a tunnel junction. The tunnel junction comprises one layer of a first conductive type and one layer of a second conductive type, both of which are thinner than one layer of a first conductive type and one layer of a second conductive type, which encompass the first active zone. The tunnel junction permits the vertical stacking of the active zones, whereby the light that is generated by the element can be increased without increasing the size of the light source.
EP-A-0 727 830 relates to a method for producing a light-emitting diode (LED) with a plurality of layers comprising adjacent first and second layers, which are connected to a connecting piece. Production can be carried out according to the wafer-bonding method. Multiple LED structures can be connected with other layers if the intermediate layer is designed such that a high degree of electrical conductivity through the element is ensured. The type of doping in the layers of the upper LED structure corresponds to the type of doping in the layers of the lower LED structure. Thus the two LED structures are arranged with the same polarity relative to one another. The surfaces to be bonded to one another (wafer bonding) should be very highly doped. When the structures are bonded, a highly doped tunnel junction with opposite polarity of the LED's is formed. As an alternative it is proposed that the tunnel junction is grown epitaxially.
From WO-A-00/77861 a semiconductor structure with active zones is known, comprising a plurality of active layers that are selective for various wavelengths, which layers are arranged in a vertical stack on a substrate, so that the incident light is able to pass through the layers with evenly decreasing band gaps. In this, photons of differing energy are selectively absorbed or emitted by the active layers. Contact elements are arranged separately on the outer sides of each layer or a set of layers having the same parameters, in order to remove the charges that are generated in the photon-absorbing layers, and/or to introduce charge carriers into the photon-emitting layers. This element is intended for use, for example, in displays or solar cells.
EP-B-0 649 202 relates to a semiconductor laser and the method for producing it. The semiconductor laser comprises a plurality of semiconductor chips sandwiched by soldering them one on top of another such that their laser emission surfaces are arranged coplanar relative to one another, with each laser chip having a substrate with epitaxial layers applied thereon, including one active layer.
From WO 99/57788 a further light-emitting semiconductor device of the type described above is known. In this publication a dual-color light-emitting semiconductor device is described, which has, between its front side and its back side, a first surface-emitting light-emitting diode with a first active zone, which emits radiation of a first wavelength, and a second surface-emitting light-emitting diode with a second active zone, which emits radiation of a second wavelength, wherein between the two active zones a first reflective layer is arranged, which is reflective for the first wavelength and is transparent for the second wavelength. It is further provided that between the second active zone and the back a second reflective layer is arranged, which is reflective for the second wavelength. The reflective layers result in improved utilization of the light from both diodes that is radiated in the direction of the back and are preferably formed from a multilayer system of layers with alternating high and low refractive indices, wherein the layers are preferably constructed from a semiconductor material adapted to a lattice.
In the prior art semiconductor device, the active zones are applied to two opposite surfaces of a substrate, so that a beam of light emitted from the lower active zone must pass through the substrate and at least one reflective layer, whereby optical losses are possible. Furthermore, with the known light-emitting semiconductor device, only two light beams can be generated. Thus its use in a colored display is limited.